1. Field of the Invention
The present invention relates generally to electrical switching apparatus and, more particularly, to arc chutes of circuit breakers. The invention also relates to arc chutes for electrical switching apparatus and to electrical switching apparatus having arc chutes.
2. Background Information
Circuit breakers and other electrical switching apparatus (e.g., without limitation, circuit switching devices and other circuit interrupters such as contactors, motor starters, motor controllers and other load controllers) typically include a set of stationary electrical contacts and a set of moveable electrical contacts. The stationary and moveable contacts are in physical contact with one another when it is desired that the circuit breaker provide electrical current therethrough to a load. When it is desired to interrupt the circuit, however, the moveable contacts are moved away from the stationary contacts, thus removing the moveable contacts from physical contact with the stationary contacts and creating a space therebetween.
The movement of the moveable contacts away from the stationary contacts results in the formation of an electrical arc in the space between the contacts beginning at the time the contacts are initially separated. Such an arc is undesirable for a number of reasons. For one, it provides a pathway for current to flow through the circuit breaker to the load when it is desired to isolate the load from such current. Additionally, the electrical arc extending between the contacts often results in vaporization or sublimation of the contact material itself, eventually resulting in destruction or pitting of the moveable and stationary contacts. It is thus desired to eliminate any such arcs as soon as possible.
The moveable contact is typically mounted on an arm that is contained in a pivoting assembly which pivots the moveable contact away from the stationary contact. An arc chute is provided along the path of the arm to break up and dissipate such arcs. Such arc chutes typically include a plurality of spaced apart arc plates mounted in a wrapper. As the moveable contact is moved away from the stationary contact, the moveable contact moves past the ends of the arc plates, with the arc being magnetically urged toward and between the arc plates. The arc plates are electrically insulated from one another such that the arc is broken up and extinguished by the arc plates. Examples of arc chutes are disclosed in U.S. Pat. Nos. 6,703,576; 6,297,465; 5,818,003; and 4,546,336. Generally, in operation in an air circuit breaker, for example, the stack of arc plates divides-up the arc voltage in the circuit breaker in order to extinguish the arc and produce a current-limiting effect, thereby providing downstream protection. This cools the arc and splits the same into series arcs. Cooling, in turn, results from arc attachment to the arc plates. Arc cooling also depends on the gas flow over the plates (e.g., convection) and hot gas removal out of a vent in the circuit breaker housing.
Arc plate geometry, the number of plates within the arc chute, and other parameters, such as spacing between arc plates, have evolved over the years as attempts have been made to provide optimum arc dissipation. Additionally, many arc chute designs employ devices such as, for example, an arc horn, or other structure which is specifically designed to draw the arc into the arc chute. See, e.g., U.S. Pat. No. 6,417,474. An arc horn generally comprises an extension of an arc plate which is bent or otherwise directed toward the direction in which it is desired to coax the arc. Such devices are most often present on the first arc plate among the stack of arc plates in the arc chute, and are designed to draw the arc away from the separable contacts, upward into the other arc plates. However, the arc has a tendency to follow the inside edge of the arc chute adjacent the separable contacts which can cause heavy erosion of the arc plates and damage to the nearby separable contacts.
There is, therefore, room for improvement in arc chutes for electrical switching apparatus, and in electrical switching apparatus having arc chutes.